Andrzej Gniewek

PEPPSI‐Type Palladium Complexes Containing Basic 1,2,3‐Triazolylidene Ligands and Their Role in Suzuki–Miyaura Catalysis

A series of PEPPSI-type palladium(II) complexes was synthesized that contain 3-chloropyridine as an easily removable ligand and a triazolylidene as a strongly donating mesoionic spectator ligand. Catalytic tests in Suzuki-Miyaura cross-coupling reactions revealed the activity of these complexes towards aryl bromides and aryl chlorides at moderate temperatures (50 °C). However, the impact of steric shielding was the inverse of that observed with related normal Nheterocyclic carbenes (imidazol-2-ylidenes) and sterically congested mesityl substituents induced lower activity than small alkyl groups. Mechanistic investigations, including mercury poisoning experiments, TEM analyses, and ESI mass spectrometry, provide evidence for ligand dissociation and the formation of nanoparticles as a catalyst resting state. These heterogeneous particles provide a reservoir for soluble palladium atoms or clusters as operationally homogeneous catalysts for the arylation of aryl halides. Clearly, the substitution of a normal N-heterocyclic carbene for a more basic triazolylidene ligand in the precatalyst has a profound impact on the mode of action of the catalytic system.

Liquid crystals for photonic applications

In this paper we describe application of liquid crystals in optical imaging and processing. Electrically and optically addressed liquid crystal spatial light modulators are key elements in real-time holographic devices. Their implementation for beam steering and hologram formation is briefly discussed. The Joint Fourier transform optical correlator for pattern recognition is presented as well as the use of liquid crystals for the adaptive optics purposes is discussed.

Palladium(II) Complexes with Small N-Heterocyclic Carbene Ligands as Highly Active Catalysts for the Suzuki–Miyaura Cross-Coupling Reaction

Four new palladium(II) complexes of the type [Pd(NHC)2X2] with N‐heterocyclic carbene (NHC) ligands of relatively small steric hindrance were prepared and characterized by using spectroscopic and X‐ray methods. For [Pd(bmim‐y)2Br2] (bmim‐y=1‐butyl‐3‐methylimidazol‐2‐ylidene), crystals of both cis and trans isomers were obtained. All the studied complexes demonstrated very high activity in Suzuki–Miyaura cross‐coupling in ethylene glycol, which yielded turnover numbers of up to 760 000. High activity was also observed if NaBPh4 was used instead of PhB(OH)2, and the best results (turnover number=580 000) were obtained with [Pd(emim‐y)2Cl2] (emim‐y=1‐ethyl‐3‐methylimidazol‐2‐ylidene). In the reaction mixture, different forms containing [Pdx(NHC)y]+ fragments (x=1–4, y=2–5) were identified by using ESI‐MS. In the presence of Suzuki–Miyaura reaction substrates, catalytic palladium intermediates with aryl groups—[Pd(NHC)2Ph]+ and [Pd3(NHC)4Ph]+—were detected. Additional mechanistic investigations, such as TEM observations and mercury poisoning experiments, substantiated the formation of nanoparticles as a catalyst resting state. These heterogeneous particles serve as a reservoir for soluble palladium species—atoms or clusters that function as homogeneous catalysts for the Suzuki–Miyaura reaction.

A chloro-bridged dinuclear phosphinitopalladium complex, di-mu-chloro-bis[(diphenoxyphosphinite-kappaP)(diphenoxyphosphinito-kappaP)palladium(II)].

The title compound, [Pd2(C12H10O3P)2Cl2(C12H11O3P)2], consists of a dinuclear mu-chloro-bridged palladium unit with two diphenoxyphosphinite groups per Pd atom, linked together by a hydrogen bond. The asymmetric unit contains one half of the molecule, with the other half generated by an inversion centre. The geometry around the P atoms may be described as distorted tetrahedral. Adjacent molecules of the complex are linked by weak C-H...O and C-H...Cl hydrogen bonds. The structure is additionally stabilized by pi-pi stacking interactions between the aryl rings. These interactions form a herring-bone pattern in the crystal structure.

4,4,5,5-Tetra­methyl-1,3,2λ5-dioxa­phospho­lan-2-one

The five-membered ring in the title compound, C6H13O3P, exists in an envelope conformation with one of the ring C atoms at the flap position. The coordination geometry around the P atom is a distorted tetrahedron. The crystal structure is stabilized by several weak C—H⋯O and P—H⋯O hydrogen bonds, forming a three-dimensional network.

Carbonylative Suzuki Coupling Reaction Catalyzed by a Hydrospirophosphorane Palladium Complex

A Pd complex with the H‐spirophosphorane ligand, PdCl2{P(OCMe2CMe2O)OC6H4NH2} (Cat. 1), was used as the catalyst in the carbonylative Suzuki coupling of substituted iodobenzenes with arylboronic acids and with sodium tetraphenylborate. Substituted diarylketones were obtained in good to excellent yields and a selectivity over 95 % under 1 atm of CO with 1.5 mol % of the catalyst. The promoting role of the H‐spirophosphorane ligand in the catalytic process was evidenced. We used X‐ray photoelectron spectroscopy, TEM, and 31P NMR spectroscopy to reveal that during the reaction Cat. 1 undergoes transformation into Pd complexes that bear the spirophosphorane ligand or other P ligands formed by its dealkylation and to Pd nanoparticles. All these Pd species contribute to the high productivity of the system.

cis-Dichlorido[2,3-dimethyl-3-(4,4,5,5-tetra­methyl-1,3,2λ5-dioxaphospho­lan-2-yl­oxy)butan-2-olato-κ2O,P]oxido(triphenyl­phosphane-κP)rhenium(V)

The title compound, cis-[Re(C12H24O4P)Cl2O(C18H15P)], was prepared from the analogous trans isomer [Głowiak et al. (2000 ▶). Polyhedron, 19, 2667–2672] by a trans–cis isomerization reaction. The ReV atom adopts a distorted octahedral coordination geometry. Besides being coordinated by the oxide and the butanolate O atoms, the ReV atom is coordinated by a pair of chloride ligands and two P atoms in cis positions with respect to each other. In the crystal, adjacent molecules are linked by weak C—H⋯Cl interactions, forming a three-dimensional network.

Chlorido(1,2-dimethyl-1H-imidazole-κN3){2-[(diphen­oxy­phosphan­yl)­oxy]phenyl-κ2C1,P}palladium(II)

The Pd atom in the title compound, [Pd(C18H14O3P)Cl(C5H8N2)], adopts a slightly distorted square-planar coordination geometry, with the metallated carbon positioned trans to the Cl atom. The crystal structure is stabilized by several weak C—H⋯O and C—H⋯Cl hydrogen-bond interactions. One of the phenyl rings is disordered over two almost equally occupied sites.

cis-Dichloridobis[tris­(2-methyl­phen­oxy)phosphane-κP]palladium(II)

In the title compound, [PdCl2(C21H21O3P)2], the Pd atom adopts a slightly distorted square-planar coordination geometry, with pairs of the equivalent ligands in cis positions. Adjacent molecules are linked by weak C—H⋯Cl hydrogen bonds. The crystal structure is additionally stabilized by π–π stacking interactions between the aromatic rings [shortest centroid–centroid distance = 3.758 (4) Å].

trans-Dichloridobis(3,5-dimethyl-pyridine-κN)(ethano-lato-κO)oxido-rhenium(V).

The title compound, [Re(C2H5O)Cl2O(C7H9N)2], was crystallized from ethanol. The crystal structure of this complex contains a Re(V) atom in a slightly distorted octahedral coordination geometry with pairs of equivalent ligands in trans positions. Adjacent complex molecules are linked by weak C—H⋯Cl hydrogen bonds. The crystal structure is additionally stabilized by π–π stacking interactions between the aromatic rings with centroid–centroid distances of 3.546 (4) Å.